Purification of crude anthracene



used in the past.

Reissued Dec. 16, 1930 UNITED STATES PATENT OFFICE.

ALPHONS O. J AEGER, OF MOUNT LEBANON, PENNSYLVANIA, ASSIGNOR TO THE SELDEN RESEARCH & ENGINEERING CORPORATION, OF PITTSBURGH, PENNSYLVANIA, A

CORPORATION or DELAWARE PURIFICATION OF CRUDE ANTHRACENE -No Drawing. Original No. 1,693,713, dated December 4, 1928, Serial No. 247,260, filed January 16, 1928.

Application for reissue filed February 26, 1930. Serial No. 431,622.

This invention relates to the purification of various grades of anthracene by processes which include solvent purification steps.

In the past crude anthracene has been purified by various solvent methods involving recrystallization or leaching. These methods have been based primarily on the use of solvents which possess greater solvent power for the impurities, such as phena-nthrene and carbazol, than they do for anthracene, especially at lower temperatures. A number of solvents have been proposed. One class consists in solvents such as solvent naphtha which have a relatively high solvent power for phenanthrene with a lower solvent power for anthracene and carbazol. This type of solvents cannot be used alone to produce high grade anthracene because of their lack of suflicient solvent power for carbazol. Another class of solvents the pyridines, have achieved considerably greater success in the past. Pyridine possesses a high solvent power for carbazol and phenanthrene and low solvent power at low temperatures for anthracene and is the most successful solvent to be Pyridines, however, are open to a number of very serious disadvantages. In the first place, their odor is eX- tremely unpleasant, their price is very high, and it is difiicult to obtain complete recovery of the solvent by simple means since pyridine is relatively soluble in Water and steam dis- 'tillation processes are therefore relatively unsuitable.

The present invention is based on the use of a new class of solvents, namely liquid compounds containing the furane nucleus.

iii \O/ These compounds possess extremely high solvent power for carbazol and phenanthrene and while capable of dissolving anthracene at elevated temperatures possess extremely low solvent power for anthracene at low temperatures. While the invention generally includes the use of all the liquid furane compounds, it has been found that some of the compounds are more advantageous than others. Thus, for example, furane itself has the serious disadvantage that it boils at about 32 C. which renders its use difiicult unless greatcare is taken to prevent loss of solvent by evaporation. The homologues of furane, such as methyl furane, and especially dimethyl furane are much more satisfactory as they have a higher boiling point. Some of the'esters of furoic acid (pyromucic acid) such as the ethyl, propyl, butyl and amyl furoates may be used.

We have found, however, that the most effective and preferred furane solvents are the aldehydes furfural and its homologues, such as methyl furfural. These products have extraordinarily satisfactory solvent powers, they are high-boiling liquids, and possess relatively very low solubility in water at low temperatures, permitting recovery of the last traces of solvent by distillation with superheated steam. Furfuryl alcohol has desirable solvent characteristics and is included in'the present invention but labors under the disadvantage that it is miscible with water. The preferred furane solvents, such as the furfurals, possess so low a solubility for anthracene at low temperatures that it is possible to obtain by their use in a minimum number of recrystallizations, washings or leachings from 94:100% of the crude anthracene in the form of purified material of excellent properties. By. reason of the fact that anthracene, phenanthrene; and carbazole all occur in the pure form as small crystals which tend to pack together, particularly in the presence ofmoisture, this purified material separates out upon removal of the solvent in the form of a cake, which is generally termed a filter cake or press cake. When the solvent is distilled off from the impurities these also separate out as a cake for the same reason and can be subjected to further treatment in the other waste products, and their relatively pleasant odor, high boiling point and relative insolubility in water render them almost ideal for the purification of anthracene. The pure furane compounds may be used or the technical grade, such as crude furfural, may be employed and are, of course, much cheaper. 1

By the use of furane solvents alone efiective purifications of crude anthracene may be carried out. Thus, for example. when a crude anthracene, containing 31.1% anthracene, 15.8% carbazol and the remainder phenanthrene and dead oils, is recrystallized resultingproduct contains 81.53% anthracene and 7.81% carbazol, the remainder being phenanthrene. The recovery of anthracene is about 96%. 7 Al second recrystallization from furfural produces a 94.35% anthracene, which contains 2.25% carbazol. The recovery of anthracene on this second recrystalhza tion is almost100% The solvent power of furfural for anthracene is extremely low but when a material istreated containing large amounts of phenanthrene, apparently the phenanthrene exerts a solvent action on the anthracene for the recovery of anthracene from the crude product in the first crystalli zation is considerably; smaller than in the second.

While the use of furane solvents alone, such as the furfurals, eifectively purifies crude .ant-hracene it is desirable in many cases to apply the process to a semi-refined anthracene with a lower phenanthrene content so as to avoid losses of anthracene due probably to solvent action of phenanthrene as described above and also to decrease the amount of furane solvent required. Such semi-refined anthracene, containing 57-62% anthracene, 3235% carbazol, with the remainder phenanthrene, can be obtained by treatment of crude anthracene with phenanthrene solvents, such as benzol, toluol, solvent naphtha,

from the chlorine purification of light oil and the like. The preliminary refining may be effected eitherby'a recrystallization process or by a'washing or leaching process. The

semi-refined anthracene when subjectedto recrystallization from crude or refined furturals using a m n mum amount of solvent at C. followed by cooling yields a purified anthracene containing 97% anthracene which is well suited for producing dye stuifs.

This shows clearlv the excellent carbazol solvent powersof furane solvents and especially furfurals. The cake obtained after distilling'off the furfural mother liquor can be purified by treatment with sulfuric acid with or Without the presence of a solvent inert toward the acid'which will eliminate any traces of anthracene present. On dilutionan albustion of carbazol.

ample, benzol, toluol, solvent naphtha, and from furfural, either pure or technical, the

and carbazol. This may be purified catalytically or may be subjected to any suitable treatment to separate the phenanthrene and carbazol. For example, it maybe subjected to fusions with caustic potash with or withoutadditions ofcaustic soda, either in an.

ordinary fusion or in the presence of indifferent diluents, such as kerosene and other hydrocarbons,both alifatic and aromatic.

Although some of the furane solvents, such as furfurals, are relatively cheap when com-.

pared to the other solvents, such as pyridine, they are nevertheless sufliciently costly and make the high recovery of thesolvent ,economically desirable. The main lo'sses when using hi gh boiling furane solvents result from the solvent which is retained in the cakes in anthracene or phenanthrene and carbazol.

From these cakes the solvent may be removed by washing with other solvents. Particularly in thecase of furfurals which show a relatively small solubility for water, the cakes may be blown with superheated steam or with any other vaporswhich tend to form with the solvent azeotropic mixtures. Othersuitable methods of solvent recovery may, of course,

be used.

In the above.description the action of the hen such mixed solvents are used, the fufurane solvents have been described as if they acted purely as indifferent solvents. It is probable. that for the most part this may be" the case but the tremendous solubility of carbazol and also of phenanthrene in the furane solvents, particularly furfurals, may be due to the formation .of loose chemical compounds with the solvent and it should be understood that the inventionis not limited to any theocific examples which illustrate theapplication of the invention.

Ewample 1 100 parts by weight of crude anthracene containing 31.1% anthracene, 15.8% carbazol,

and the remainder phenanthrene and dead oils, are stirred in 400O parts by weight of furfural, methyl furfural, or a mixture of the two, and the mixture is heated up to 80 (J. and then allowed to cool to 1520 C. An thraccne crystallizes out and after separating from the mother liquor and drying the recrystallized product constitutes 39.5 parts by weight and analyzes 81.53% anthracene, 7.18% carbazol and the remainder phenanthrene. It will appear, therefore, that more than 95% of the crude anthracene is recovcred. The furfural can be distilledofi from the mother liquor which contains phenanthrene and carbazol and further recovered from the'anthracene cake by blowing steam.

therethrough. Recoveries up to 97.5% are ossible and may be increased up to 99% by lowing superheated steam through the phenanthrene cake also.

The phenanthrene-carbazol cake obtained after recovery of furfural can also be treated with or without the presence of solvent naphtha or other indifferent solvents with KOH ora mixture of KOH and NaOH at a temperature of 150250 C. Alkali metal carbazol forms and can be separated from the phenanthrene resulting in the recovery of a high grade carbazol and a high grade phenanthrene. Instead of using causticpotash fusion, the phenanthrene-carbazol mixture may be submitted to the action of solvents, such as solvent naphtha, benzol orthodichlorbenzol and other chlorinated solvents which have a high solvent power for phenanthrene or do not readily dissolve carbazol.

Instead of recovering phenanthrene, carbazoland furfural from the crude cake, the latter may be uniformly vaporized with air and catalytically oxidized to products such as phthalic anhydride, maleic acid, mesotartaric acid and the like. In this oxidation reaction, both phenanthrene and the furfural are effectively used and in some cases a considerable amount of carbazol may also be transferred into usable intermediate oxidation products which will usually include maleic acid.

Instead of using furfurals in the above example, other furane solvents, such as dimeth l furane or furfuryl alcohol, maybe used but the furfura-ls give better results and are considerably cheaper.

Example 2 Anthracene recrystallized from furfural as described in Example 1 is subjected to a second crystallization 'from' furfural using 3-4 parts of furfural to "one part of anthracene and heatedup to 80 C. followed by cooling to 15-20 C. The product obtained 'contains 94.35% anthracene and 2.25% carbazol. The recovery of anthracene is practically quantitive.

E ma/mple 3 Centrifu ged crude anthracene, containing 26.09% anthracene, 15.25% carbazol and the remainder phenanthrene and dead oils, is recrystallized from a minimum amount of toluol which will dissolve. the crude anthracene at 80 C. A recrystallized anthracene is obtained which contains 56.71% of anthracene and 26.64% of carbazol, the remainder being phenanth-rene. 100 parts of this recrystallized anthracene are put on a filter and gradually washed with 2 3 times the amount of technical furfural. A high grade anthracene containing 94% anthracene and 3.2%v carbazol is obtained, theremainder being probably phenanthrene. This anthracene is only slightly colored.

. Example 4 Various grades of crude anthracene are treated with benzol, toluol, solvent naphtha, acetone, gasoline, orthodichlorbenzol, or other chlorinated solvents for phenanthrene. The treatment is continued until substantially all of thephenanthrene is removed.

It is possible to obtain in.this way an anthracene containing 63.8% anthracene and 36.2% carbazol. Thiscrude anthracene is then recrystallizedfrom fur'fural using the minimum amount of furfural'necessary to dissolve the mixture at 80 C., followed by cooling down to 15 C. An anthracene is obtained which contains 97.76% anthracene and'2.24% carbazol. The mother liquor can be distilled off and a carbazol cake remains which contains only traces of anthracene which can be readily removed by treatment with 98% sulfuric acid at 2025 C., with or without the presence of inert solvents followed by dilution with water which results in the precipitation of carbazol which is 99.6%

pure. 1 1 Example 5 8-10 parts of 100% KOH or an equivalent least one furfural. v 1

amount of KNO I The suspensionis coated onto 200 parts by volume of pea size'puinice fragments and heated in a current of air at 350400 C. The crude anthracene described above is uniformly vaporized in air in proportionof 1 part crude anthracene by weight to 25-35parts of air and then passed over the contact mass at 380 (l A purified;

anthracene is obtained which contains 7 5.34 anthracene and 0.96% carbazol, the remainder being mainly phenanthrene This material is then recrystallized from the minimum amount of furfural. ,ne'ec ed to "dissolve the mass at C. and is then Washed or leached with. furfural. After this treatment, the product analyzes 99.2% anthracene,- the re- 'mainder being phenanthrene. I

anthracene and 18-22% carbazol is uniformly vaporized with air in the ratio of'l :35 to 1:50 by weight and passed over the contact mass: at 380-.400 C. a purified anthracene is obtained which contains 60.3% anthracene and 6.4% 'carbazol', the remainder being phenanthrene. Thispurified anthracene is then submitted to recrystallization from furfural using 250 parts offurfural to 83 parts of anthracene. 'After recrystallization, the anthracene obtained contains 93.04% anthracene and 2.42% carbazol with the remainder phenanthrene, The recovery of anthracene is from 9395% of the anthracene contained in vthe material subjected to recrystallization. A very high grade p'henanthrene can berecovered from the mother liquor. I l

' I claim:

l. A method of purifying impure anthi'acene, which comprises subjecting it to the selective solvent action of a solvent containing at least one liquid compound containing the furane nucleus.

. 2, .A method of purifying impure anthracene, which comprises subjecting it torecrystallization from a solvent containing at least one liquid compound containing the furane nucleus. v I I 3. A method of purifying impure anthracene, which comprises subjecting it to the selective solvent action of a solvent contain ing at leastone furfural.

4. A method of purifying impure anthracene, which comprises subjecting it to recrystallization from a solvent containing at 5. A method' of purifying crude anthracenescontaining as their main impurities canbazol and phenanthrene in a two-step process-,one of, the steps comprising subjecting the material tothe selectivesolvent action of a liquid compound containing a'furane nucleus and theother step comprising the subjection .of the Jnttellfll (to the selective solvent action ofa solvent which dissolves phenanthrenereadily but which has small solvent power for carbazol and anthracene. I

6.3}A method according to claim 5, in which the crude anthracene is first subjected to treatment with'the phenanthrene solvent and the purified anthracene from this step is then subjected to the action of a solvent containing a ,furane nucleusL; I I 7. A method according to claim 5; in which the crude anthracene is first subjected to treatment with the phenanthrelle solvent and the purified anthracene from this step is then subjected to the actionof a' solvent containing a furfural. I v v 8." A method of-purifying crude anthracene containing as impurities phen'anthrene and vent, whereby the "phenanthrene 'an'drcar bazol is brought into solution and the anthra cene isrecovered in the form of a cake and recovering the I furfural from the bake by steam distillation 9. A method of purifyingcrude anthracene containing asimpurities phenantl rene and carbazol, which comprises subjecting it to the selectivesolventaction of a furfural solvent, whereby the phenanthrene and carbazol are brought into solutionand the anthracene is recovered in theform of a cake and recovering the furfural from the cake by displace ment with another solvent." I j 10. A method ofpurifying crude anthracene, which comprisesfs-ubj ecting it to the ac-'* tion of a'mixed solvent containing a furane nucleus and a solvent having specific solvent power for phenanthrene.

cleus'andcooling the solution toa temperature not greater thanroom temperature and separating the anthracene which crystallizes out from the mother liquor. I

13. A- method of, purifying an impure anll. A method of purifying crude anthrathracene, which comprises dissolving it at a temperature between room temperature and the boiling'point of the solvent in a minimum amount of furfuraliaiid cooling the solution to a temperaturenot greater than room tem perature and separating the anthracene which crystallizes out from the mother liquor.

14. A method of recovering pure anthracene and phenanthrene from crude anthra- 5 cene which comprises subjecting the crude anthracene to the selective solvent action of a solvent containing a furane nucleus whereby phenanthrene and carbazol are separated from the anthracene, recovering the phenanthrene and carbazol from the solvent and subjecting the mixture to a caustic alkali fusion treatment followed by vaporization of the phe nanthrene.

15. A method of purifying anthracene containing as impurities at least one substance included in the group consisting of phenanthrene and carbazole, which comprises subjecting it to the selective solvent action of a solvent containing furfural,

whereby the anthracene is recovered in the form of a cake and recovering the furfural from the cake by steam distillation.

16. A method of purifying anthracene containing as impurities at least one substance included in the group consisting of phenanthrene and carbazole, which comprises subjecting it to the solvent action of a furfural in amounts to' separate at least part of the anthracene in the form of a cake and subjecting said cake to steam distillation.

17. In methods of purifying anthracene substances whereby a cake is obtained containing a furfural, the step which comprises subjecting said cake to steam distillation.

3s 18. In methods of purifying anthracene substances whereby a cake is obtained containing anthracene and a furfural, the step which comprises subjecting said cake to steam distillation.

40 19. In methods of purifying anthracene containing phenanthrene and carbazole as impurities by the action of solvents containing furfural such that a cake is obtained containing at least part of the anthracene together with at least one of the substances included in the. group consisting of phenanthrene and carbazole, the step which com prises recovering the furfuralfrom said cake by steam distillation.

20. A method of purifying anthracene containing as impurities phenanthrene and carbazole, which comprises subjecting it to the selective solvent action of a furfural, whereby the phenanthrene and carbazole are brought into solution, evaporating said solution, and recovering it whereby a cake is obtained consisting substantially of carbazole and phenanthrene, and recovering the furfural from said cake by steam distillation.

Signed at Pittsburgh, Pennsylvania, this 21st day of February, 1930.

ALPHONS O. JAEGER. 

